An engine exhausts heat energy while generating torque by combustion of fuel, and the coolant absorbs the heat energy while circulating through the engine, a heater, a radiator, and the like and discharges the absorbed heat energy to outside.
When a temperature of the coolant of the engine is low, viscosity of oil may increase to increase frictional force and fuel consumption, and a temperature of an exhaust gas may increase gradually to lengthen a time for a catalyst to be activated, which degrades quality of the exhaust gas. In addition, as a time required for a function of the heater to be normalized is increased, a driver may feel discomfort.
When the coolant temperature is excessively high, since knocking occurs, performance of the engine may deteriorate by adjusting ignition timing in order to suppress the knocking. In addition, when a temperature of lubricant is excessively high, a viscosity is lowered such that a lubrication performance may be deteriorated.
For sufficient cooling of an engine and heat exchange elements, a thermostat or a control valve for controlling coolant flows are provided.
When the thermostat or the control valve malfunctions so that a temperature of coolant is raised excessively, a fail-safe thermostat is opened for protecting and the engine and so on.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.